In relatively small turbine engines in airborne environments, fuel flows at high altitudes, particularly during starting, are frequently quite low. Consequently, fuel injectors requiring high fuel pressures are commonly used to achieve pressure atomization of the fuel. However at low turbine speeds, it is difficult with available fuel pumps to generate the necessary fuel pressure. Further at such low speeds, the compressor of the turbine will not be delivering a large volume of compressed air and the atomization assist resulting from air blast atomization of fuel is unavailable. By way of example, in a typical worst case, the pressure drop across the combustor is about one inch of water which ordinarily is insufficient to provide acceptable fuel atomization.
To meet these difficulties, conventional injectors have extremely small orifices to provide the desired atomization making them precision formed parts. They are thus costly to manufacture. At the same time, because of the very small orifices employed, they are prone to plugging, a factor that clearly detracts from reliability. Where swirl pressure atomizing fuel injectors are used, with viscous fuels, high losses occur which reduce atomization efficiency and atomization is frequently unsatisfactory.
The present invention is directed to overcoming one or more of the above problems.